Challenge 3 — Solution

Task: Write a function createInventory() returning an object with
addItem(name, qty), removeItem(name), and getCount(name) methods,
all closing over a private object that the caller can never access
directly. Add a few items, remove one, and confirm getCount
reflects the changes.

function createInventory() {
    const items = {};

    return {
        addItem(name, qty) {
            items[name] = (items[name] || 0) + qty;
        },
        removeItem(name) {
            delete items[name];
        },
        getCount(name) {
            return items[name] || 0;
        }
    };
}

const inventory = createInventory();

inventory.addItem("apples", 10);
inventory.addItem("bananas", 5);
inventory.addItem("apples", 3);

console.log(inventory.getCount("apples"));    // 13
console.log(inventory.getCount("bananas"));   // 5

inventory.removeItem("bananas");
console.log(inventory.getCount("bananas"));   // 0

console.log(inventory.items);                 // undefined — no direct access


Expected output:

13
5
0
undefined


Notes:
- items[name] = (items[name] || 0) + qty handles both "first time
  adding this item" (items[name] is undefined, so || 0 kicks in) and
  "adding more to an existing item" in one line.
- getCount uses the same || 0 fallback so asking about a removed or
  never-added item returns 0 instead of undefined.
- inventory.items is undefined because items only exists inside
  createInventory's closure — the returned object exposes three
  methods, never the underlying data structure itself.